It has been known for many years that plastic materials may be shaped by heating the material to a temperature at which it may be easily deformed, and then bending or otherwise shaping the material into the desired configuration. It has also been known that pre-stretched plastics have a particular response to heating. When pre-stretched plastic materials are heated above their deformation temperature, the material is known to shrink in size.
One of the known ways for heating plastic material in order to shrink it is to expose the plastic material to microwave radiation. For this purpose, the plastic material has to come in contact with a microwave susceptible material. The microwave susceptible material is heated up when exposed to microwave energy and transfers this heat to the plastic material.
U.S. Pat. No. 4,985,300 discloses a heat shrinkable film useful for packaging and for cooking in a microwave oven of at least one food item which requires surface browning or crisping, comprising at least one layer of flexible, heat resistant, microwave transparent base film, which is shrinkable, and a transmissive layer of microwave susceptor material extending over the base film. The film is suitable for browning or crisping of a food item placed adjacent thereto. Under the influence of microwave radiation the packaging material shrinks to the size of the food item wrapped into the packaging material and transfers its heat to the food in order to create a brown or crispy surface on the food item. The packaging material, after being exposed to microwave energy, is generally discarded and not used, for example, as a bin for serving the food. The hot food item is typically unwrapped, i.e. the shrunken packaging material is removed, prior to serving of the food item.